This invention relates to polyurethane coatings, especially upon resilient, embossed vinyl sheet floor covering materials, from compositions which can be rapidly cured using a combination of heat, produced for example by infrared radiation ("IR"), and actinic radiation especially ultraviolet ("UV") radiation; then exposed to the action of isocyanate-reactive substances, such as moisture, to convert a predetermined content of isocyanate groups in the polyurethane into urea groups.
The prior art has disclosed polyurethane coating compositions, and vinyl sheet coated therewith, wherein the coating composition consists essentially of low molecular weight resinous urethane polymers (often called in the art "oligomers" or "prepolymers"), terminated by isocyanate groups and curable at elevated temperatures by action of moisture; and as an improvement on these coating compositions, compositions curable entirely by actinic radiation (particularly UV) consisting essentially of photopolymerizable ingredients, including an unsaturated resinous compound (preferably a urethane oligomer) having at least two photopolymerizable ethylenically unsaturated groups per molecule (preferably of the acrylic type), a photo reactive monomer, a multifunctional monomer solvent and crosslinking agent, and a photoinitiator (U.S. Pat. No. 4,100,318, col. 2, lines 42-50 and col. 11, lines 32-50 of McCann et al. for Actinic Radiation Cured Coating for Cushioned Sheet Goods and Method). More particularly, this patent discloses such coating compositions based on acrylourethane oligomer from isophorone diisocyanate and hydroxyethyl acrylate; plus a monomeric acrylate, a glycol diacrylate and a photoinitiator; and cured by exposure to UV radiation (Example II at col. 14, and col. 19, line 3-col. 20, line 14).
U.S. Pat. No. 4,216,267 of Aug. 4, 1980 to Lorenz et al. for "Flexible Substrates Containing A Radiation Curable Coating Composition" is of interest for its exemplification of radiation curable acrylourethane compositions derived from specifically isophorone diisocyante or 4,4'-dicyclohexylmethane diisocyanate (Examples 1-3, 5,7-11,13-16).
U.S. Pat. No. 3,935,330 of Jan. 27, 1976 to O. W. Smith et al. for "Two-Step Coating Process" is of interest in disclosing coating compositions curable by irradiating in one step and heating in a second step. These coatings consist essentially of (1) a "thermoset crosslinker" such as a polyfunctional epoxide or urea-formaldehyde or melamine-formaldehyde reaction product (col. 7, lines 2-6); (2) a reactive solvent sensitive to both thermal and radiation crosslinking such as acrylates of monofunctional or polyfunctional alcohols e.g. 2-hydroxyethyl acrylate; trimethylol propane mono or diacrylate, pentaerythritol mono-or di-or triacrylate, or "urethane oligomers containing both an (OH) group and a (CH.dbd.C) group" (col. 7, lines 56-63 and col. 8, lines 24,26-28, 37-38, 43-50); and (3) a radiation sensitive component such as isodecyl acrylate, 1, 4-butanediol diacrylate and trimethylol propane triacrylate (col. 8, line 55--col. 9, lines 14-15, 21-23). Also "small amounts of other crosslinkable polymers" (col. 10, line 7) can be used including "known polyureas and polyurethanes" (col. 10, line 67-68).
A valuable innovation is set forth in U.S. patent application Ser. No. 023,107 of S. N. Varadhachary et al., filed Mar. 23, 1979 now abandoned. A conventional or an acrylo-modified polyurethane resin provides available isocyanate groups and a vinyl resin includes a chemical compound possessing hydroxy or other isocyanate-reactive groups. When the resins are exposed, while in contact, to curing conditions there is sufficient chemical inter-reaction between them to create a strong and permanent primary chemical bond between them. In particular, in Example I, an acrylated polyurethane resin and a glycol diacrylate are employed in a coating composition, providing 1.93 weight percent of available NCO therein, which is applied to a wet thickness depth of about 1.5 mils (0.04 mm) upon the polyvinyl chloride wear layer of a foamed, chemically embossed polyvinyl chloride composite sheet; which wear layer composition contains about 11% by weight of a linear polyester having hydroxyl value of 107 mg. KOH/g, i.e. hydroxyl equivalent weight of 523 (available commercially as Oxyester T 1136 (V)); and the coating is cured by passage through a UV unit.